Oh my this is so funny. Thanks for brightening my day.
The problem with counting back, etc is that students learn how to do give change when they are young, but as they grow there is really no opportunity for them to practice this learned skilled in real life situations. Parents pay for everything, and then typically with a credit/debit card. There are few neighborhood stores where children would be appreciated to shop on their own, something I believe was more prevalent in days gone by.
By the time the children are high school/college age the skill is lost, or not really needed. Many young adults of that age too have debit/credit cards paid for by their parents. I'm sure if they learn how to use the machines properly they will survive just fine, and leave us to our chuckles.